Most semiconductor and related products, such as transistors, diodes, light emitting diodes, MEMS devices, planar waveguide structures, and integrated circuits, are fabricated in the form of a large number of elements manufactured simultaneously on a large workpiece, such as a wafer. This wafer is typically composed of Si, GaAs, GaP, InP, sapphire, or other material, or combinations thereof. The creation of devices is most often performed using conventional fabrication techniques such as photolithography, oxidation, implantation, deposition, etching, epitaxial growth, and/or spin coating. Upon completion of these device-laden wafers, the individual devices must be singulated, a process which is typically referred to as “dicing.” The individual devices are referred to as “die” or “dice.” The area on the wafer in between active parts of adjacent die is referred to as the “street” or “dice lane.” The streets are limited to a minimum street width because of the wafer material that is removed or destroyed during the dicing process. The wafer area that is completely removed by the dicing process can be called a “cut area” or “kerf,” while the rest of the street must accommodate any damage zone around the cut area and any misalignment or deviation from straightness of the cut.
Historically, dicing has been performed by the use of a wafer saw or by the technique of “scribe and break,” where the wafer is notched, often by a diamond point, and is then cleaved along this scribe line. Due to issues with scribe and break such as low yield, dicing saws became the predominant tool for dicing wafers. Conventional slicing blades typically have a narrow dimension of about 50 to 200 μm along their cutting axes and produce cuts that are wider than the blades. The slicing blades currently need to be this wide to withstand stresses of making straight cuts through the strength and thickness of conventional wafers, for example. The wide cuts made by the mechanical cutting blades significantly reduce the number of rows and columns of die that can be fit onto each wafer.
Desire to reduce the cut area led to the exploration of the use of lasers in the dicing process. Lasers offered the potential of the smallest street width available, due to a potentially very small kerf width and the possibility of accurate alignment of the laser to the workpiece. Thus, laser sawing was an attractive alternative to the conventional techniques for dicing. However, laser separation of the wafer material was much slower than done by blade so the street size generally remained large enough to accommodate the width of dicing blades, which could be used as a second step after laser scribe lines were formed. A number of these hybrid laser and dice blade processes were developed; however, the street width still remained relatively large. U.S. Pat. No. RE 43,400 discusses the advantages of employing lasers to separate device-laden workpieces.
Advances in laser parameters and processing techniques have reduced the throughput time and cost of separating the wafer material without the use of mechanical saws, such as the dice blades. Nevertheless, laser-dicing processes can be further improved.